Keywords: Functional/Dynamic, MSK, wrist, low-field, real-time

Motivation: A thorough understanding of wrist kinematics and kinetics is essential for diagnosing and treating wrist pain and instability. Current MRI methods are limited to tracking just a few thick slices and therefore use hand supports to restrict motion to pre-selected, simplified orientations.

Goal(s): To develop a 3D real-time MRI method at 0.55T for comprehensive evaluation of wrist kinematics.

Approach: A bSSFP 3D stack-of-spiral sequence with long spiral readout was implemented for evaluating wrist kinematics during maneuvers. 

Results: Comprehensive 3D coverage at 10 frames/second was achieved without any restriction on wrist motion, providing measurements of ligament intervals in 3D and during active wrist motion.

Impact: The proposed 3D real-time method can potentially improve diagnosis of wrist injury and dysfunction and treatment planning, by providing a unique 3D evaluation of wrist kinematics and kinetics during the performance of clinically-important maneuvers involved in activities of daily living.

Keywords: Osteoarthritis, Bone, Patella, Shape, ACL, PTOA

Motivation: PTOA progression is poorly understood and there is a relative dearth of data available on the impact of the patellofemoral joint on PTOA.

Goal(s): The goal of this study was to elucidate the relationship between PTOA, knee function, and patella shape and to investigate possible indicators for PTOA progression.

Approach: A shape model of the patella was used to explore longitudinal shape changes and associations with injury, sex, KOOS, and cartilage T1rho in 67 patients following ALR and 11 controls.

Results: Ipsilateral patella shape was found to be associated with ACL injury, sex, and the degenerative changes accompanying PTOA.

Impact: This study suggests patella shape may play a role in ACL injury and PTOA. These results should inform future biomechanical studies of the knee joint which could lead to the development of preventative orthoses and novel interventions.

Keywords: Osteoarthritis, MSK, shape model, MOAKS, osteophytes

Motivation: Osteoarthritis is a whole joint disease that requires quantification, localization, and visualization of disease related features of bones and cartilage.

Goal(s): To develop a novel neural shape model (NSM) that can encode and reconstruct bone and cartilage shape, while quantifying localized features of OA.

Approach: We trained a NSM on 6,325 knees and compared its reconstructions to a conventional statistical shape model and its ability to predict localized disease to a convolutional neural network.

Results: The NSM reconstructed tissues with cartilage thickness correlations >0.993. NSM representations accurately diagnosed OA and predicted localized severity of osteophytes and cartilage defects better than a CNN.

Impact: Our NSM can reconstruct whole bone and cartilage morphology, while encoding localized pathology specific information. Research use of the NSM can unlock novel insights into OA pathophysiology. Clinical deployment would enable automated insights into whole joint health.

Keywords: Whole Joint, Molecular Imaging, Knee, Pain

Motivation: Diagnosis of chronic knee pain remains a challenge with conventional diagnostic methods leading to unsatisfactory treatment in a large group of patients.

Goal(s): To investigate the use of sigma-1 receptor (S1R) radioligand, [¹⁸F] FTC-146 in conjunction with positron emission tomography/magnetic resonance imaging (PET/MRI) for identifying the pain generator in chronic knee pain.

Approach: Comparison of [¹⁸F] FTC-146 PET-MRI imaging findings in patients with unresolved chronic knee pain to healthy volunteers.

Results: All 15 patients showed statistically significant increased uptake of S1R compared to healthy control subjects in a variety of locations. At sites of abnormal PET uptake, MRI often did not demonstrate abnormalities. 

Impact: Future clinical implementation of S1R-PET/MR can potentially help reveal previously unidentified pain generator in patients with chronic knee pain that have exhausted standard clinical care leading to better-targeted treatment. 

Keywords: Cartilage, PET/MR

Motivation: Whether the compositional, metabolic, and biomechanical relationships have a mediated effect on one another is the next crucial step toward decoding the isolated PFJOA mechanism.

Goal(s): To investigate whether the relationship of morphological-joint-degradation with SUV-values from ¹⁸NaF-PET and cartilage-T₂ in isolated-PFJOA are mediated by gait-biomechanics.  

Approach: Linear regression was performed between (i)WORMS_BME(predictor) vs. Medial-SUV_max, Lateral-SUV_max (outcomes), and (ii) WORMS_Cartilage(predictor) vs. Mean-T_{2-Deep-Medial}, T_{2-Superficial-Medial}, T_{2-Deep-Lateral}, T_{2-Superficial-Lateral} (outcomes) patellar and trochlear. For significant correlations, mediation analyses were done to examine the role of Normalized-Mean-Peak vGRF_IP as a mediator.

Results: WORMS_BME vs. Medial-SUV_max, Lateral-SUV_max relationships are mediated by gait; WORMS_Cartilage vs. Mean-T_{2-Deep-Medial}, T_{2-Superficial-Medial}, T_{2-Deep-Lateral}, T_{2-Superficial-Lateral} aren’t mediated.

Impact: This is the first step towards understanding the flow of causalities and mediated interrelationships of bone remodeling (SUV), morphological degradation (WORMS), cartilage loss (T₂), and gait biomechanics in a complex joint developing isolated PFJOA

Keywords: Other Musculoskeletal, Artifacts, Bloch Simulator, Metal Artifacts, Implant

Motivation: Commonly used methods for the quantification of metal-induced image artifacts, such as measuring the extent of signal voids, do not capture spatial frequencies of ripple artifacts, as seen in dedicated metal artifact reduction sequences including SEMAC or MAVRIC. 

Goal(s): To propose a new method for the quantification of SEMAC ripple artifacts which may serve as quality metric for sequence optimizations. 

Approach: We applied a k-space-based metric to MR Bloch simulations of SEMAC sequences with variable slice thicknesses and RF pulse shapes (time-bandwidth product, TBW).

Results: A trend towards higher absolute artifact intensity and lower spatial frequency can be observed for higher TBWs.

Impact: The proposed metal artifact metric extends current quantification methods by taking the spatial frequency distribution of ripple artifacts into account. This may serve as a basis for metal artifact reduction sequence optimization, with a particular focus on RF pulse parameters.

Keywords: Osteoarthritis, Perfusion, Embolization

Motivation: Embolization, a new treatment for chronic joint pain, may be more clinically effective when treatment is targeted using pre-procedural dynamic contrast-enhanced (DCE)-MRI.

Goal(s): Assess presence of synovitis and identify culprit arterial vessels using pre-procedural DCE-MRI.

Approach: Representative patients with mild-moderate osteoarthritis of the shoulder, hip and knee underwent fat-suppressed DCE-MRI using CDT-VIBE.  Imaging was performed with high temporal (6-7 sec/frame) and spatial (0.6 mm isotropic interpolated) resolution with 3-minute acquisition and 5cc/sec contrast injection.

Results: DCE-MRI readily identifies regions of synovitis and its contributory arterial vessels.  By exploiting contrast kinetics whole-joint synovial volumes can be semi-automatically calculated.

Impact: MRI-targeted joint embolization therapy has the potential to result in improved pain and functional outcomes with reduced side effects.  Rapid calculation of whole-joint synovial volumes may enable their use as a biomarker of arthritis severity and embolization treatment response.

Keywords: Osteoarthritis, DSC & DCE Perfusion, Synovium

Motivation: A precise method to quantify the degree of synovial inflammation in patients with knee osteoarthritis (OA) is needed to evaluate response to new disease modifying treatments in clinical trials.

Goal(s): To evaluate the repeatability of quantitative dynamic contrast enhanced (DCE) MRI derived biomarkers for synovitis quantification in the whole synovium and synovial subregions.

Approach: Test-retest study comprising DCE-MRI at baseline and 1 month follow-up in knee OA patients. Vessel mapping was used to determine synovial subregions.

Results: DCE-MRI biomarkers have good test-retest repeatability in both the whole synovium and synovial subregions, with Ktrans showing the best performance.

Impact: Quantitative DCE-MRI can provide precise biomarkers for synovitis quantification in knee osteoarthritis. Subregional evaluation using vessel mapping is an important tool for more precise treatment response evaluation in clinical trials with targeted local interventions, such as selective arterial embolization.

Keywords: Bone, Ischemia

Motivation: Relaxation time mapping may be clinically useful to inform the severity of ischemic injury to bone marrow in osteonecrosis of the femoral head.

Goal(s): To compare the temporal response of T2, adiabatic T1ρ, and adiabatic T2ρ mapping to acute ischemic injury to the femoral head.

Approach: 24 piglets were imaged using 3D relaxation time mapping at 3T MRI before and after surgical induction of unilateral femoral head ischemia. Corresponding cellular changes were evaluated histologically.

Results: T2 and adiabatic T2ρ were the most sensitive in detecting acute injury to the femoral head, as early as 24 hours after onset of ischemia.

Impact: T2 and/or adiabatic T2ρ relaxation time mapping can potentially address a clinical need for a non-contrast-enhanced imaging technique to establish the severity and extent of bone marrow necrosis in the earliest stages of osteonecrosis of the femoral head.